1. Field of the Invention
The present invention relates to a rendition control apparatus, which controls a rendition by compressing or expanding the time axis of waveform data (time stretching) to generate a reproduction waveform.
2. Description of the Related Art
Conventionally, in the field of electronic instruments, e.g., samplers are used, which sample the actually rendered phrase into waveform data without changing it, to reproduce a group of continuous tones, such as a complete melody or a part thereof (in the following, "a group of continuous tones, such as a complete melody or a part thereof" is also called "a phrase") with an electronic instrument,.
In Japanese Patent Application (Tokugan) Nr. H10-205482 with the title "Apparatus for Controlling the Rendition of Waveform Data" (application date: Jul. 21, 1998), the applicant to the present application has presented a technique for imparting effects, such as swinging, on waveform data by compressing or expanding the waveform data on the time axis, in which a sampler is used that samples a phrase into waveform data without changing it.
The technique disclosed in Japanese Patent Application Nr. H10-205482 pre-stores, for each set of waveform data, control signals for imparting effects, such as swinging, on the waveform data (referred to simply as "control signals" in the following), the control signals being optimized for the corresponding waveform data. With these control signals, the rendition control apparatus compresses or expands the waveform data on the time axis and reproduces the waveform data.
Because the technique disclosed in this Japanese Patent Application Nr. H10-205482 includes storing a control signal for each set of waveform data, the control signals are characterized by a precise synchronization with the phrase, regardless of fluctuations in the tempo of the sampled phrase.
Other conventional rendition control apparatuses that are known in the related art control renditions by pre-storing a continuous sound waveform and compressing or expanding the stored sound waveform on the time axis to generate a reproduction waveform. One such rendition control apparatus is disclosed in Japanese Patent Application Nr. H10-55180, which proposes a technique for controlling a swing rendition. With this technique, a sound waveform is prestored, and expansion and compression on the time axis are performed by reading out the former half of the waveform within periods, into which the stored sound waveform has been segmented periodically depending on note length, at a relatively slower speed, and the latter half at a relatively faster speed, whereby a swing is imparted on the reproduced musical sound. The publication explains that a plurality of variation patterns of the read-out speed necessary for reading out the waveform are arranged, a pattern is selected from this plurality of patterns, and always applied to the same phrase, whereby several different rhythms can be achieved.
It is further mentioned that during the reproduction of the sound waveform, the user can switch between those variation patterns of read-out speed to achieve several different rhythms. Here, a continuous sound waveform or phrase means a rhythm or a melody based on a string of a plurality of tones, wherein one or more bars of rhythm or melody are usually regarded as one phrase.
Because the technique disclosed in the aforementioned Japanese Patent Application Nr. H10-205482 stores a control signal for each set of waveform data, a large storage region is necessary for storing these control signals.
Also, for a simultaneous sound production with a plurality of waveform data simultaneously using the technique disclosed in this Japanese Patent Application Nr. H10-205482, it is necessary to produce the same number of control signals as there are sets of waveform data for the sound production, which makes the processing complicated. In other words, because in the technique disclosed in this Japanese Patent Application Nr. H10-205482, the processes for multiple simultaneous sound production is complex and complicated, and the processes for the compression and expansion of the control signal are also complex and complicated, the load on the digital signal processor (DSP) becomes too large if these processes are performed by a DSP.
Moreover, when a phrase is rendered on an actual instrument, the timing of the rendition often differs slightly with each beat, and even when the same phrase is repeated, there are usually slight differences of timing for each rendition, and to reproduce a sound waveform with a swing rendition it would be preferable to provide a function allowing for such a rendition, as this would enable a natural rendition. But with the technique disclosed in the aforementioned Japanese Patent Application Nr. H10-55180, it is only possible to apply a selected pattern uniformly to a complete phrase, or the user can simply select a variation pattern manually. In these publications, there is no suggestion of providing the rendition with slight differences in the timing over the passage of time as described above, when applying a swing to a musical sound. Moreover, there is no suggestion of changing the reproduction tempo of the sound waveform when applying these slight timing differences.